1. Field of the Invention
The present invention relates to a projection display, and more particularly, to a projection display which can be self-powered or can be externally powered.
2. Description of the Prior Art
In a projection display, how to prolong the lifespan of a light bulb is of primary concern. The quality of a heat-ventilating device is one of the most crucial factors affecting the lifespan of the light bulb.
Since light bulbs generate heat, even for a time after a light bulb is turned off, prior art projector heat-ventilating devices do not stop functioning when the light bulb is turned off. Instead, the heat-ventilating device still functions for a certain period of time to ventilate the heat generated by the light bulb as completely as possible, and to protect the light bulb from heat damage.
For example, U.S. Pat. No. 6,704,061 entitled “Temporary Simulated Off State in a Restart of a Video Display” to Gilmore et al. teaches a two-stage management flow chart to control the operation of a heat-ventilating device. In operation, when a user presses a power off key, a display panel performs a pseudo power-off operation, that is, the display panel stops displaying images during a first time period beginning at a moment when the power off key is pressed, to inform the user that the power off key is pressed. During the first time period, the light bulb is still fully shining. If any key is pressed during the first time period, indicating that the press of the power off key was in error, the display panel re-displays images under a circumstance that the light bulb need not be re-actuated (the above is a first stage). On the contrary, if during the first time period no key is pressed, indicating that the user means to power off the projection display, the management flow chart enters a second stage. During the second stage, the management flow chart ignores any key press, that is, the management flow chart dumps any key signals. During the second stage, the light bulb's energy dies off, while the heat-ventilating device does not stop functioning until the end of the second stage.
The above-described management flow chart of controlling the heat-ventilating device after the power off key is pressed does not end until the end of the second stage, so as to cool off the light bulb as completely as possible. However, the management flow chart is not able to handle a situation in which the projection display is suddenly deprived of power. In the case of a sudden power outage, the heat-ventilating device stops the heat-ventilating operation, and the light bulb can be easily damaged by the heat remaining in the projection display.